1. Field of the Invention
The present invention relates to a device and a method used in a communication system, and more particularly, to a device and a method of handling soft information.
2. Description of the Prior Art
Orthogonal frequency-division multiplexing (OFDM) (or termed as discrete multi-tone modulation (DMT) technique) is adopted in various modern high-speed communications systems for transmitting and receiving signals due to its high bandwidth efficiency and robustness against fading, to increase a probability of recovering the signals correctly. Various numbers of bits can be allocated on subcarriers according to the OFDM, to use channel capacity efficiently.
In general, when a communication system using an OFDM is operated, part of subcarriers is used for channel estimation, such that a receiver can obtain channel responses (e.g., channel frequency responses) corresponding to all the subcarriers via the part of the subcarriers, to use the estimated channel responses for recovering transmitted symbols (e.g., data) on the subcarriers. In detail, a transmitter allocates reference signals known by the receiver on the part of the subcarriers. The reference signals are transmitted with data signals to the receiver, when the transmitter transmits an OFDM signal formed by all subcarriers. After receiving the OFDM signal, the receiver can use the reference signals to estimate the channel responses (abbreviated as the reference channel responses) corresponding to the subcarriers for transmitting the reference signals, and can also estimate the channel responses (abbreviated as the data channel responses) corresponding to the subcarriers for transmitting the data signals according to the reference channel responses. Thus, after estimating the data channel responses, the receiver can use the estimated channel responses for signal processing operations, such as equalization, demodulation, decoding, etc., to recover the data signals.
However, an allocation of the reference signals is usually not perfect or specific subcarriers are subject to greater interferences, so that accuracies of the data channel responses of different subcarriers are different. The accuracies of the data channel responses are even with considerable differences, e.g., the accuracies are particularly low, such that performances of the equalization, the demodulation and the decoding are affected. Thus, how to reduce the effect of the channel responses caused to the receiving performance is an important problem to be solved.